Character mistake: When Walter brings Cynthia's dog in the carrier to the bowling alley he refers to it as a Pomeranian while it is actually a terrier. Somewhat related, when the the Nihilists confront Dude in the bathtub, the dude refers to the ferret as a marmot. Walter later refers to the ferret as an amphibious rodent. Perhaps he was thinking of a mink.

When the Dude is in Jackie Treehorn's estate, he pencils over a pad of paper to see what Jackie wrote down while he was on the phone. He then hurriedly crumples up the piece of paper and shoves it in his wallet. Then, when we see the Chief of Police of Malibu looking through the contents of The Dude's wallet, the paper is there, neatly folded in fourths.

At the beginning of the movie, when The Dude is writing a check for the cream at the grocery, look at the date on the check. Sept 11, 1991. A few seconds later we see George Bush Sr. talking about Iraq. So here we have a scene containing Sept. 11th, George Bush and references to the Middle East in a movie that takes place in 1991.